Electropolishing bath solution

ABSTRACT

A PRINCIPALLY PHOSPHORIC ACID ELECTROPOLISHING BATH FOR COPPER BERYLLIUM WIRE IS CHARACTERIZED BY ADDITIONS OF SMALL AMOUNTS OF COPPER SULFATE AND AMMONIUM SULFATE (OR OF COPPER AMMONIUM SULFATE), AND SODIUM MOLYBDATE, AND A FLUOBORIC ADDITIVE.

United States Patent ()fice 3,738,922 ELECTROPOLISHING BATH SOLUTION Emil Toledo, Natick, Mass, assignor to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Jan. 20, 1972, Ser. No. 219,512

Int. Cl. C23b 3/06 U.S. Cl. 204-1293 4 Claims ABSTRACT OF THE DISCLOSURE A principally phosphoric acid electropolishing bath for copper beryllium wire is characterized by additions of small amounts of copper sulfate and ammonium sulfate (or of copper ammonium sulfate), and sodium molybdate, and a fluoboric additive.

BACKGROUND OF THE INVENTION This invention relates to the art of electropolishing wire and more particularly to an improved electropolishing bath for use in preparing the surface of copper beryllium wire for subsequent copper coating and/or plating with magnetic recording material in the making of magnetic memory system wire. One example of the type of process in which electropolishing is practiced is described in US. Pat. No. 3,556,957.

Existing electropolishing baths have been subject to one or more problems including selective attack or etching of cobalt beryl, temperature sensitivity, current density sensitivity, short life, copper ion concentration in solution, and tendency to pit certain lots of raw wire under all conditions.

While baths composed principally of phosphoric acid and having lesser ingredients such as sulfuric acid, chro-v mic acid, and halogen material, all as exemplified by the mentioned US. Pat. 3,556,957, have been used with considerable success, they have been subject to the aforementioned problems. Use of sodium molybdate in comhination with a fluoborate material such as fluoboric acid overcame the problem of selective attack or etching of cobalt beryl.

Recently stock of phosphoric acid became very low, and it was necessary to use electropolishing baths for two days instead of one between replacement, and also a somewhat weaker phosphoric acid formulation was used. Surprisingly, instead of the rapid deterioration of properties as had been experienced with the usual 90% phosphoric acid bath, a more rapid metal removal rate as well as a moderately superior surface were observed on the second day of use. Experimentations with various additions in the form of salts of heavy metals such as tungsten and molybdate were tried and also experiments on additions of copper as copper sulfate, copper ammonium sulfate, and copper nitrate were carried out and overcame the other problems.

SUMMARY OF THE INVENTION With the foregoing in mind, it is an object of this invention to provide an improved electropolishing bath with excellent surface preparation properties, good reproducibility, and a longer useful life.

As another object of this invention is the provision of an improved electropolishing bath for use with copper beryllium wire preparatory to coating and/or plating as mentioned earlier and which solves the combined problems of selective attack of cobalt beryl, temperature sensitivity, current density sensitivity, short life, copper ion concentration in solution, interdependence and tendency to pit certain lots of raw wire.

3,738,922 Patented June 12, 1973 Yet another object is the provision of an improved electropolishing bath of the foregoing character which is characterized by small quantities of a fluoborate material, sulfuric acid, sodium molybdate, and copper ammonium sulfate in substantially an phosphoric acid solution.

Preferably the bath contains addition of a fluoborate material in the form of fiuoboric acid, and additions of small amounts of sodium molybdate and sulfuric acid.

While the amounts of the foregoing material additions to the basic phosphoric acid solution can be varied somewhat depending upon the current densities employed, bath temperatures, and the like, the preferred embodiment of electropolishing bath according to this invention has constituents falling within the ranges specified in the following tables:

Distiled water to make Replacement of prior baths with bath made according to the foregoing formulations have resulted in the ability to produce an excellent wire surface at high metal removal rates with great consistency. Moreover, use of the new bath has materially improved yield while substantially increasing the useful life of the bath.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. it is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An electropolishing bath of the type having phosp'horic acid as the major component and a fluoborate material and sulfuric acid as minor components for use in electrolytically removing metal from a wire formed of coppper beryllium as it passes through the bath, said bath being characterized by the improvement comprising:

addition of minor amounts of copper and of ammonium sulfate; and r a minor addition of soditun' molybdate.

2. An electroplating bath as defined in claim 1 and wherein the mentioned ingredients are substantially in the following percentages:

Percent Phosphoric acid 85 Fluoboric acid .2 to 1.0 Sulfuric acid .2 to 1.0 Sodium molybdate .2 to 1.0 Copper sulfate .2to1.0 Ammonium sulfate .2 to 1.0

Distiled water to make 100%.

3. An electropolishing bath as defined in claim 1 and wherein said copper and said ammonium sulfate are added together as copper ammonium sulfate.

4. An electropolishaing bath as defined in claim 1 and wherein the mentioned ingredients are substantially in the following percentages:

Percent Phosphoric acid 85 Fluoboric acid .2 to 1.0 Sulfuric acid .2 to 1.0 Sodium molybdate .2 to 1.0 Copper ammonium sulfate .2 to 1.0

References Cited UNITED STATES PATENTS THOMAS M. TUEARIELLO, Primary Examiner 

